Surgical access for superficial structures such as the eye, skin or teeth present little challenge. However, for treatment of pathology deep in the body, the surgical approach may risk violating or potentially injuring several healthy tissues in the process of reaching the surgical target. In addition, an optimal surgical route would not place any vital structures at risk when at all possible. Because, however, the spinal column lies deep in the very center of the body, it presents unique challenges for surgical access to its pathologic targets. Posteriorly, spinal surgical access must traverse multiple anatomic planes and deep layers of muscle. Anteriorly and laterally, besides the muscular impacts, approaches also frequently engage multiple vital structures in the passage between the skin and the target. These anatomic realities by necessity create a major part of the overall risk and morbidity for the patient, as well as more technical challenges for the surgeon.
Pathology in the cervical spine is ubiquitous and commonly includes herniated disc, stenosis, disc degeneration, facet disease, tumor, trauma and other instabilities. The majority of cervical problems requiring surgery occur between C2 and T1, and currently there are two common surgical approaches for accessing this region—the anterior and the midline posterior approaches. See FIG. 10. While both are commonly utilized, each has significant drawbacks and unique morbidities that should ideally be overcome due to their common application.
1. Current Approaches: Description, Advantages and Problems
A. Anterior Approach
The patient is positioned supine and the surgical team is standing throughout the procedure. A three to four centimeter incision is placed either on the left or right medial boarder of the sternocleidomastoid, with the plane of dissection passing medial to the carotid sheath. Incisions are normally placed transversely and are extended slightly when access to more than two vertebral bodies is necessary. A vertical incision is usually utilized when more than 3 vertebral bodies need to be accessed simultaneously, with this incision being five or more centimeters in length. By necessity, the carotid sheath must be mobilized laterally and the esophagus, thyroid, trachea, and larynx are mobilized medially. This is mostly an inter-muscular plane of dissection with muscular damage being limited to the platysma and the omohyoid superficially, and the longus colli deep on the anterior aspect of the spine. Collectively, this amount of muscular disruption is typically considered relatively insignificant. However, there are several vital structures in the route of this dissection. Airway retraction and manipulation or post-op swelling can lead to post-op airway obstruction which can be fatal in rare cases. This has lead to many adjustments in retraction and ET cuff management but the potential still exists, particularly in prolonged cases. The carotid artery and internal jugular vein can be injured during the approach or plaques dislodged from the carotid in older patients potentially resulting in a stroke. Additionally, vocal changes postoperatively can occur due to significant retraction or scarring of the larynx or unintended injury to the laryngeal nerves, especially the recurrent, which is potentially in the plane of dissection. Furthermore, dysphagia is frequent after this approach from swelling, scarring and the required esophageal retraction. This dysphagia, often resolves over several months but can be extremely troublesome for daily function and can result in permanent difficulty with eating and even aspiration. Other important nerve structures at risk include the sympathetic trunk which lies on the anterior aspect of the longus colli (Horner's syndrome) and the hypoglossal nerve if the exposure is extended to C4 or above. The superior, middle and inferior thyroid arteries and veins are directly in the field of approach and must be controlled as well, representing one of the other potential causes of rare but life threatening post op airway obstruction from hematoma.
Once the spine is reached, the surgeon has excellent access to the disc. However, it becomes necessary to remove the entire anterior longitudinal ligament and the disk structure itself in order to reach the typical pathologies at the posterior aspect of the disc space, as well as gaining access to the spinal canal and the nerve roots in the foramen. Consequently, when decompressions of the spinal cord or nerve roots is required from an anterior approach, some type of motion segment reconstruction is usually mandated due to the subsequent lost of motion segment integrity that is required through this route. This means that virtually every standard anterior cervical approach results in some type of arthroplasty or fusion to reconstruct the loss of motion section integrity that may be entirely secondary to the approach (even if fusion was not indicated by the patient's original pathology). Anterior disc without fusion was done in the 1960s-70s but now have been abandoned. This is in sharp contrast to current treatment the lumbar spine where surgeons commonly perform posterior decompressive procedures without any fusion or reconstruction, since that anatomic route of approach does not create enough disruption to mandate some type of reconstruction as an aftermath. Besides increasing the need for fusion, the anterior cervical approach also presents another challenge in that if nerve compression is located laterally, the exposure will be limited by the uncovertebral joint, and more significantly, the vertebral artery. Injury to this vital structure can occur with dissection in the foraminal area or if reconstruction deviates off the midline. Vertebral artery injury can potentially be catastrophic.
The anterior cervical exposure usually requires self retaining retractors, which can occasionally injure the esophagus or the sympathetic trunk if they migrate out of position. For this reason an assistant is often required to stabilize retractors in their position, and assistance is also often necessary in accessing the contra lateral side of the exposure and in maintaining orientation to the midline during reconstruction. Typically this exposure can be extended up to C3 and down to C7 or T1 depending on the position of the clavicle. Even with nasotracheal intubation, the mandible can occasionally obstruct clear access to the upper cervical area. When revision is required after the anterior cervical approach, access is often done on the contra-lateral side due to major challenges with scaring around all the vital structures on the side of prior approach, making revision on the ipsilateral repeat dissection potentially risky.
Only pathology in the anterior aspect of the spine and the anteromedial foraminal region can be visualized through this approach.
Primary advantages to this approach are universal surgeon familiarity, quick and easy dissection for the surgical team, very limited muscle damage, and minimal post operative surgical pain with quick return to function for the uncomplicated patient.
Primary problems associated with the approach include putting several vital structures at risk in the approach route, potential for rare but catastrophic complications, dysphasia, limited foraminal access, and almost always requires extensive reconstruction or fusion.
B. Posterior Midline Approach:
The patient is positioned prone with the surgical team standing throughout the procedure. The main difference versus the anterior approach is that there are virtually no vital structures at risk in this surgical route, but extensive muscle detachment, dissection, and disruption is mandatory. This approach utilizes a midline vertical incision and requires detachment of all three layers of cervical musculature. The superficial, intermediate, and deep layers are all detached and dissected from the tip of the spinous process down across the deep surface of the lamina to the lateral aspect of the lateral mass. This involves detachment of the longissimus, spinalis, trapezius, semi spinalis, splenius, multifidus, rotatores and rhomboid at C7. Because of the bulk and depth of these combined posterior cervical muscles, the dissection usually extends at least 1 level above and below the target level just to gain adequate access at the ends of the required field. This can create risk of damage to healthy motion segments. Although this is a “subperiostial” exposure, all of these muscles are detached, and exposure of the lateral mass usually disrupts the dorsal ramus at the dissected levels either directly or through the position of the deep retractors. Self retaining retractors (Cerebellar or other) are required, and these by necessity exert significant pressure on the muscle structures due to the depth and bulk of these posterior cervical muscles. This retractor pressure can result in ischemic necrosis of the muscle tissue bilaterally. Additionally, the midline ligamentous structures (ligamentum nuchae and the interspinous ligaments) are usually detached, which disrupts the integrity of the entire posterior musculo-ligamentous system in the cervical spine. Additionally, as these muscular structures span multiple segments, this cervical posterior exposure can potentially impact muscular and ligamentous function far beyond the extent of the approach, by injuring structures that span from the occiput to the upper thorasic region.
Once the deep cervical spine is exposed, the surgeon has good access to the dorsal elements and the spinal canal. Midline laminectomy or other dissection can be done as well as foraminal dissection. The limits of the thick muscular retraction laterally creates some restriction for far lateral exposure. The working angle that the surgeon has provides excellent opportunity for placing lateral mass instrumentation, but creates significant challenges for placing cervical pedicle screws where the converging angle of the instrumentation is at odds with the thick lateral musculature. Access to antero-lateral pathology such as herniated disc can be accomplished although there are limitations to what can be done on the floor of the spinal canal due to considerations of spinal cord safety. It is noteworthy that the structures best accessed through this approach are the spinous processes, while in fact virtually no significant pathologies are recognized in this midline area.
As is seen in the lumbar spine (and in contrast to the anterior cervical approach), posterior cervical access often does not require a fusion, and lends itself to decompressive laminectomy or forminotomy procedures without fusion or reconstruction when appropriate. This approach has also been expanded to include laminoplasty although post op muscular pain and stiffness has been a problem. Closure of this multi-muscular incision requires multiple deep layers and is sometimes challenging both cosmetically as well as in achieving excellent re-approximation of each anatomic level.
Problems associated with this approach include extensive deep muscular and ligamentus disruption, difficult bilateral retraction, significant often prolong post operative incisional pain, difficult convergence angle to pedicles and referred pain from injury of soft tissue structures.
Advantages of this approach include surgeon familiarity, no vital structures in the surgical route, no catastrophic potential approach complications and finally, it, does not demand fusion as an aftermath in many situations.
Approach-Related Prior Art
The literature suggests that there are substantial problems and potentially disproportionate problems related to the anterior approach. Although the anterior approach is quite commonly used, popular and widely accepted, there are obviously ongoing issues that need to be addressed. A survey of the activity in the literature would suggest that perhaps the posterior approach has either created less difficulties or at least garnered less attention with respect to potential complications. While recognizing that both approaches have important clinical utility, their deficiencies do suggest a need for improvement and perhaps indicate a rationale to look into the posterior surgical approach options that seem to have a better safety profile with less potential for catastrophy. There will always be some needs for both, as the surgical approach must “go where the pathology is” but we may be able to improve the safety profile of many cases.
While the typical posterior approach has been almost universally utilized via the midline, there have been exceptions that have allowed for creation of postero-lateral or lateral cervical approaches that will be outlined below, although none of them mimic in any way the procedure that we have described.
In 2009 B. Zhao, Spinal Journal 9:822-829 2009 described a posterolateral exposure for excision of extra foraminal tumors. However, this utilizes a traditional midline incision and a standard medial to lateral exposure out to the lateral mass, detaching all the muscles in a standard approach. Further extension of their dissection is then taken by detaching the Levator scapulae and the scalene muscles to provide access to the brachial plexus and anterior structures. Thus, the plane of dissection is exactly opposite to that which we are utilizing, and our approach intentionally spares the muscles they are detaching specifically for the purpose of protecting the brachial plexus. It would be theoretically possible, to convert our exposure to an extensile approach that would allow access to the brachial plexus and the lateral cervical spine or even anterior cervical structures. This extensile application would no longer be considered “inter-muscular” or in any way minimally invasive or tissue sparing, although it certainly may have utility in unusual pathologic circumstances.
S. J. Hyun Surgical Neurology 72:409-13, 2009 described another posterolateral approach which is based on the posterior aspect of the sternocleidomastoid. This surgical approach mobilizes the V-2 segment of the vertebral artery for access to the lateral cervical area and is particularly targeted to the very upper cervical spine. This approach does not engage in any way the plane of dissection on the posterolateral cervical spine as we have described, and remains anterior to the Scalenes.
Upper cervical and high cranio cervical posterior or far lateral approaches have been described for pathology involving the foramen magnum, clivus, and the C1-C4 region. Although these approaches do place the skin incision on the lateral cervical area, all of these techniques involved detachment of the splenius, semispinalis, and even the longissimus from the skull K. A. Tsutsumi et al Neurological Surgery 23:301-09 1995; X. G. Tong Chinese Journal of Contemporary Neurology and Neurosurgery 8:38-42 2008.). Therefore, all of these craniocervical and far posterolateral pre-cervical approaches are muscle detaching and radically different from our muscle sparing technique. Additionally, the posterolateral upper cervical approaches discussed above also involve lateral positioning of the patient, with the surgical team typically standing which are in sharp distinction to our technique. The plastic surgery literature includes descriptions of multiple flaps in the cervical area utilizing the superficial and intermediate layers for reconstruction. A splenius Capitis flap and others for reconstruction of pathologies such as Arnold-Chiari malformation have been described (Elshay etal N. I. Elshay Plastic and Reconstructive Surgery 9 3:1082-86 1994). These of course involve detachment and mobilization of muscular structures and are in no way an inter-muscular approach for cavity creation such as we have outlined. Tunneling techniques and pocket creating techniques have been widely utilized in plastic surgical strategies in the areas of the chest and the abdominal wall for various reconstructive applications although these have not been used with respect to surgery on the spinal structures themselves.
The importance of the superficial and intermediate cervical musculature that we are preserving by this new technique has been suggested in multiple areas of the literature. Panjabi et al estimated that 80% of stability of the cervical spine is muscular, with only 20% being osteoligamentous in nature (Clinical Biomechanics 1998). A 2011 study by E. Okada et al, EuroSpine Journal published online Mar. 23, 2011 Springer, with MRI evaluation showed a clear age dependent atrophy of the splenius and semispinalis which are the largest of the posterior muscles in the cervical spine. This was seen throughout all cervical levels, and highlights the critical importance of preserving as much of this muscle function as possible particularly in the middle-aged and older patients. All of the key cervical muscles described by M. S. Conley et al Spine 20: 2505-12 1995 for extension (semispinalis and splenius) and as well as for rotation (splenius, semispinalis, Levator scapuli and scalene) are all preserved by the approach that we have outlined.
A detailed anatomic study by A. Ono et al Spine 33:349-54 2008 demonstrated wide variations in anatomic insertion patterns of cervical musculature. This includes the splenius, serratus, and rhomboid. This work stresses the need to preserve tendinous attachments to the various and contiguous posterior midline structures, and emphasizes the unpredictable clinical impact of detaching these muscles from their midline insertions as is done in today's standard approaches. All of the Nuchal based musculature was felt to be critical to craniocervical function through the analysis of this study.
A. N. Vasavada et al Spine 23:412-22 1998 reported that the largest moment arms throughout the head and neck system are generated by the semi spinalis and splenius capitis in extension, and by the trapezius in axial rotation. This type of work further emphasizes the critical importance of preserving midline boney attachments of these superficial and intermediate muscular layers which is in sharp contrast to what is currently done with the standard posterior cervical exposures. The mechanical importance of the splenius muscle is further illustrated by treatments that have been described for splenius type torticollis. In such cases, approaches to the upper splenius and semispinalis have been described for the purpose of selective dennervation. This approach involves a midline based dissection with intentional sectioning of the motor branches, which is in sharp contrast to our approach which involves the approach plane from a lateral direction specifically preserving these motor branches as much as possible.
There is additional prior art with respect to elevating type retractor systems. These have been utilized primarily in the fields of plastic surgery and general surgery. The Laprolift system was described for access to the retro peritoneal space and the abdominal cavity. Its utilization was extended to be an adjunct to access to the anterior aspect of the lumbar spine. To our knowledge, there is no art suggesting cavity creation techniques or technologies for the posterior aspect to the spine such as we have described.